Corrective factor activity of normal human serum has been recovered from reconstituted precipitates of serum obtained with 70% saturated ammonium sulfate and have been found to be enriched in 0-40% fractional ammonium sulfate precipitates. Further isolation and purification will be carried out by Sephadex G-200 chromatography and polyacrylamide gel electrophoresis. Fractions retaining corrective activity will be further studied for: 1) Corrective activity on cultured fibroblasts from patients with Types I, II, and III (A & B) mucopolysaccharidoses; 2.) activity of the following enzymes: Alpha-L-iduronidase, hyaluronidase, aryl sulfatase A & B, Alpha- and Beta-N-acetylhexosaminidase, Beta-galactosidase and Beta-glucuronidase; 3.) antigenic purity and 4. antigenicity. Attention will be given to the specificity of action, its quantitation and its potential for use in clinical treatment of patients with the Hurler Syndrome.